The main objective of this project is to understand how the BCL-6 gene is regulated and how its functional interaction with the IL-6/STAT3 pathway may contribute to its role in normal B cells and B cell lymphomas. BCL-6 encodes a POZ-zinc finger type transcription represser that has been thought to repress transcription in vivo by recruiting corepressors SMRT/NCoR/BCoR and NuRD/MTA3. BCL-6 is constitutively expressed at high levels in many diffuse large cell lymphomas (DLBCL) due to genetic alterations that override a negative autoregulatory mechanism governing BCL-6 transcription. In the normal lymphoid system, high level BCL-6 protein is specifically found in B cells within the germinal centers (GC) and BCL-6 function is critical for GC formation. Our recent work indicates that BCL-6 autoregulation works in a SMRT/NCoR/BCoR-and NuRD/MTA3 independent manner. Therefore in Aim 1, we plan to characterize specific chromatin changes involved in BCL-6 autoregulation and identify the novel corepressor used by the BCL-6 protein to regulate its own transcription. Our recent study also uncovered a set of very novel findings indicating that BCL6 is a powerful inhibitor of STATS expression/activation, and that STATS is constitutively activated in the activated B cell like DLBCL (ABC-DLBCL) and required for cell proliferation and survival. Thus, experiments in Aim 2 are designed to characterize the functional relationship between BCL6 and STATS in plasma cell differentiation, determine the cause of constitutive STATS activation in ABC-DLBCL, and study the tumorigenic potential of a constitutively activated STATS in vivo. Since ABC-DLBCL is often associated with poor treatment outcome, we also plan to pursue collaborative studies to evaluate the prognostic value of STATS activation in primary DLBCL either as a single marker or in combination with BCL6. Our studies should provide valuable information regarding a novel aspect of BCL6's transrepression mechanism and more importantly, further our understanding of the roles played by BCL6 and STATS in the genetics and biology of B cell lymphomas.